Sorting machine

ABSTRACT

A number of steeply inclined tapered slides are arranged for gravity assisted singulation and alignment of items such as rice grains that are introduced at the top from vibrating chutes that are gently inclined in the opposite direction. The chutes extend from a common vibrating feed tray and have adjustable entrance gates to equalize the flow rates of the items. A stationary hopper supplies the feed tray through a flexible coupling. At the bottom of each slide, a photoelectric viewer is arranged to operate an ejector for diverting grains having dark spots. A variable background is provided and is adjusted so that the signal induced thereby is identical to that of the mid-portion of an acceptable grain. Light sources are positioned both above and below the photoelectric means so as to provide extra illumination for the leading and trailing ends of each grain, thus to avoid spurious signals similar to those induced by dark spots but caused by the rounded ends of acceptable grains.

Elite States Patent [1 Hoover et a1.

1 SORTING MACHINE [75] Inventors: Michael C. Hoover; William C. Long,

both of Houston, Tex. [73] Assignee: Mandrel Industries, Inc., Houston,

Tex.

[22] Filed: Mar. 15, 1971 [21] Appl. No.: 124,320

[52] U.S. Cl. 209/73, 209/111.6 [51] Int. Cl. B07c 1/04, B070 5/342 [58]Field of Search 209/73, 111.6, 111.7,

[56] References Cited UNITED STATES PATENTS 877,322 1/1908 Gebler226/566 3,066,797 12/1962 Fraenkel.... 209/111.6 3,179,247 4/1965 Hutter209/74 3,385,434 5/1968 Nelson.... 209/111.6 3,482,686 12/1969 Wood209/l1l.6 X

Primary Examiner-Richard A. Schacher Att0rney-Robert G. Clay 111 $73,484June 12, 1973 [57] ABSTRACT A number of steeply inclined tapered slidesare arranged for gravity assisted singulation and alignment of itemssuch as rice grains that are introduced at the top from vibrating chutesthat are gently inclined in the opposite direction. The chutes extendfrom a common vibrating feed tray and have adjustable entrance gates toequalize the flow rates of the items. A stationary hopper supplies thefeed tray through a flexible coupling. At the bottom of each slide, aphotoelectric viewer is arranged to operate an ejector for divertinggrains hav ing dark spots. A variable background is provided and isadjusted so that the signal induced thereby is identical to that of themid-portion of an acceptable grain. Light sources are positioned bothabove and below the photoelectric means so as to provide extraillumination for the leading and trailing ends of each grain, thus toavoid spurious signals similar to those induced by dark spots but causedby the rounded ends of acceptable grains.

10 Claims, 9 Drawing Figures Pmmmm 3.738.484

sum 1 on;

UH HMHHQM gunman INVENTOR.

I MICHAEL C. HOOVER ATTORNEY PAIENIEI] Jim 2 I973 SW11 2 BF 4 INVENTOR,

MICHAEL C. HOOVER flaw/a ATTORNEY PAINTED- 3 man INVENTOR.

MICHAEL C. HOOVER AI'IORNEY msmwm z 5.738.484

SIHT HIF4 "REJECT" LEVEL NORMAL I SIGNAL RANGE 40 GOOD GOOD LIGHT GRAINGRAIN MINOR MAJOR SPURIOUS DARK DEFECT DEFECT DEFECT GRAIN GRAIN SIGNALSINVENTOR.

MICHAEL G HOOVER BY flab/ea AT TOHNI. Y

E'II3 E SORTING MACHINE BACKGROUND OF THE INVENTION This inventionrelates to sorting machines and particularly to such machines adaptedfor gravity assisted singulation of the items to be sorted.

Previously, sorting machines for tiny items such as grains of rice, havecomprised rotating suction wheels or other rotation or reciprocationmechanisms for singulating (i.e. separating and aligning in serialorder) the grains for individual viewing by photoelectric means. Whilemost such machines have operated satisfactorily, their volume ortime-rate of sorting per ton is low when compared with the rate that isachievable for items of larger size. To increase the sorting rate, it isusually necessary to arrange a large number of sorters in parallel. Withrotating and reciprocating mechanisms such as are known to the priorart, the space that is required for parallel arrangement is extremelygreat and is usually out of proportion to the requirements of economyand efficiency.

Accordingly, it is an object of the invention to provide a compact highspeed sorting apparatus for small items.

It is another object of the invention to provide such a sortingapparatus that is adaptable for parallel arrangement and operation of alarge number in a small space.

SUMMARY OF THE INVENTION These and other objects are provided in anapparatus described as follows. A number of steeply inclined ta-' peredslides are arranged for gravity assisted singulation and alignment ofitems such as rice grains that are introduced at the top from vibratingchutes that are gently inclined in the opposite direction. The chutesextend from a common vibrating feed tray and have adjustable entrancegates to equalize the flow rates of the items. A stationary hoppersupplies the feed tray through a flexible coupling. At the bottom ofeach slide, a photoelectric viewer is arranged to operate an ejector fordiverting grains having dark spots. A variable background is providedand is adjusted so that the signal induced thereby is identical to thatof the midportion of an acceptable grain. Light sources are positionedboth above and below the photoelectric means so as to provide extraillumination for the leading and trailing ends of each grain, thus toavoid spurious signals similar to those induced by dark spots but causedby the rounded ends of acceptable grains.

DESCRIPTION OF THE DRAWINGS FIG. I is an elevation view partly brokenaway of an apparatus according to the invention;

FIG. 2 is a right side elevation view, partly broken away, of theapparatus of FIG. 1;

FIG. 3 is an enlarged view taken along the plane of lines 33 of FIG. 2;

FIG. 4 is an enlarged cross sectional view taken along the plane oflines 4-4 of FIG. 2;

'FIG. 5 is an enlarged view of a portion of the apparatus shown in FIG.2;

FIG. 6 is a schematic view illustrating the operation of the invention;

FIG. 7 is a view illustrating a variation of the apparatus of FIG. 5;

FIG. 8 is an elevation view taken on the plane of lines 8-8 of FIG. 2;and

FIG. 9 is a sectional view taken on the plane of lines 99 of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGS. 14 thereare shown a number of elongated, tapered slides 11, each of which has acentral longitudinal generatrix 12 steeply inclined (e.g., 35 from thevertical) for gravity assisted separation of small granular items suchas grains 13 of rice sliding downwardly thereon. In the art of sortinggranular items, it is of the utmost importanct to be able to separatethe items and space them out in serial order (i.e. singulate) so thatthey may be viewed one at a time and so that a rejection operation takeseffect only for the one grain that is defective. In the presentinvention the elongation of the slides 11 and their considerablevertical extent (e.g., about 40 inches in an actual machine) enlists theseparation assistance of gravity in the following way. It is well knownthat falling bodies accelerate at a constant and substantial rate, sothat if two bodies begin falling from the same point at slightlydifferent intervals of time, it follows that the vertical separationbetween them increases as a function of the acceleration g of gravityand the square of the time (t of fall. If two grains of rice are each025 inches long, and one begins to fall at time t and the other beginsto fall I millisecond later (i.e., at time t t .001 sec.), then when thesecond grain has fallen 40 inches, its leading end must be spaced behindthe leading end of the first grain by one-fourth inch. In other words, asuitable separation equal-to the length of one rice grain can beachieved in a fall of 40 inches even when the grains begin to fall onlyI millisecond apart in time. This minimum time-spacing is equivalent toonly about four tenthousandths of an inch (0.0004 inches) in terms ofthe initial falling distance of one grain, i.e., when the second grainbegins to fall, the first has already fallen 0.0004 inches. In 40 inchesof fall, then, the initial spacing is increased nearly 6,000-fold, from0.0004 to 0.2500 inches. The usefulness of gravity assistance forseparating the grains is therefore evident.

In the present invention, the grains are expected to slide down theinclined slides 11 rather than falling perfectly freely, so of coursethe slight frictional retardation of the grains on the slide tends todiminish the separation achievable by gravity. However, dry frictiondoes not increase substantially with velocity, so its effects may bereckoned as constant and slight. We have seen that for free fall thegrains of rice must be spaced apart for time intervals of greater than 1millisecond at the top of the slide. If the effect of friction addsmerely another millisecond to this minimum requirement, there is littledisadvantage, for by far the overwhelming bulk of grains coming into thetop of each slide 11 are spaced apart in time for greater than 2milliseconds.

Besides the above consideration, the frictional effect of the inclinedslides 11 is more than offset by the channeling effect of the taperingshape of the slide. In FIG. 3 it is shown how the slide has an'upper-endcross section of U-shape defined by two side walls 14 and a roundedbottom portion 16 of a radius much larger than the transverse radius ofa rice grain 13. About one-third of the way down from the top, the slidehas narrowed to a bottom portion just precisely fitting the rice graincross section, and the side walls have converged to define aclose-spaced generally Vshaped cross section. Clearly, then even if twograins of rice fell into the upper end of the slide 11 at times lessthan 2 milliseconds apart, they would nonetheless strike differentportions of the slide bottom and, what with the effect of impact forcesand the jostling effect produced in the grains by the tapering sides 14,the grains are still constrained to align themselves one behind theother in serial order before they reach the bottom. In fact, it may besaid that even if two grains begin their falls at precisely the sameinstant in time, it is substantially impossible for them to arrive atthe bottom end of the slide 1 1 without being suitably spaced apart inserial order.

If the grains are to derive the maximum effect from their initial timespacing, they should begin their falls from a condition of zero verticalcomponent of velocity. Also it is desirable to reduce impact effects ofthe grains in the upper end of the slides 11 as much as possible, whichrequirement calls for the smallest possible horizontal component ofvelocity as well. Ideally, the grains would drop into the upper part ofthe slide 11 from a portion of the structure (i.e., the chutes 17) inwhich they occupied a position at rest (zero velocity in any direction)at the instant immediately before the fall began. This condition isapproximately achieved by giving the chutes 17 the gentlest possibleslope downward at an inclination in the opposite direction from that ofthe associated slides 11. The minimum inclination of the chutes 17 isthe least inclination at which the grains will slidingly migratedownwardly at a reasonable processing rate when the friction is reducedas by vibrating the chutes 17, as with eccentrically loaded vibratingmotor means 18. The chutes 17 are also tapered somewhat, but still attheir open ends permit the random showering of grains into the slides11. A further effect that has been noted with this structural geometryis that bouncing grains strike one another and tend to thus' damp ordecrease the bouncing effect.

To make utmost use of the space saving structure of slides 11 and chutes12, a large number of each are arranged in parallel, and the chutes 17are mounted to extend from a common feed tray 19, from which the chutesare partitioned by adjustable gates 21. Four motors 18 are used in theillustrated device, attached to the tray 19 (only two are shown in FIG.1 Because the induced vibrating effect varies from chute to chute as afunction of mechanical and mass characteristics of the chute, anddistance of the chute from the motor, the gates 21 are adjustedindividually in actual operation until the rates of flow of grains inall of the chutes are equalized and optimum (about 50 lbs. per hour perchute).

Above the tray 19 is fixedly mounted a hopper 22 for reception of thegrains, and a flexible coupling 23 connects the stationary hopper 22with the vibrating tray 19, so that a closed conduit for the grains isformed from the upper opening 24 of the hopper to the gates 21 of thechutes 17. The slides 11 do not vibrate, nor do any other portions ofthe apparatus except the coupling 23, tray 19, chutes l7 and motors 18.

As illustrated in phantom in FIG. 2, the tapering'of the slides 17enables a double saving of space in that two full banks of slides 11 maybe criss-crossed at the narrower portions thereof, while the widerchutes 17 are divided between two opposite sides of the machine and areabutted side-by-side.

At the bottom end of each slide 11, the rice grains shoot out withconsiderable velocity upon a trajectory or path 31 (FIG. 5) which issubstantially a straight prolongation of the generatrix 12, at least inthe region of the predetermined viewing zone 32 adjacent the end of theslide. Each grain 13 is also invariably oriented with its length alongthe path 31 and is thus viewed from the same angle by a photoelectricviewing means 33 of standard type, disposed at the side of path 31 andprovided with lens means 34 to define the zone 32 of view. Because ricegrains are of generally gray-white coloring if acceptable, and aregenerally translucent, and because unacceptable grains are usuallydistinguishable by the appearance of dark spots visible from all sidesunder proper illumination through the translucent interior, it isnecessary to illuminate and inspect each grain from only one of itslonger sides. To obtain a voltage signal from the photocell 33indicative of an acceptable grain, the present invention provides alight source 35 shielded from the viewing zone 32 and illuminating agenerally gray-white background 36 which is rotatable on an axis 37abnormal to path 31 so that the background shade can be matched withthat of an acceptable grain, and the voltage level 40 of the photocellsignal is the same when an acceptable grain is in view as it is whenthere is no grain in view (FIG. 6). As shown in FIG. 5, the background36 is rotatable through about by means of a bell crank 38 operated by apin 39 sliding in a slot 41 on the bell crank and extending from apiston 42.

The illustrative apparatus is of the dark-trip type and provides apositive signal pulse 43 when a dark spot in an unacceptable grainpasses through the viewing zone 32. However if the grain is illuminatedfrom only one position adjacent the photocell 33, as is usual in theprior art, the rounded leading and trailing ends of the grain reflect alesser amount of light to the photocell 33 than comes from themid-portion of the grain. At the same time, the leading and trailingends of the grain are cutting off the reflected light from thebackground 36. The viewing zone is of course as narrow as possible andextends for a considerably less distance in the direction of path 31than the length of the rice grain, in order to obtain the maximum signallevel from the smallest dark spot. But the result of this combination ofconditions, when only a single lamp is used, is that the ends of therice grain appear as dark spots to the photocell and cause spuriousdefect signals 47 even though the grain may actually have no dark spots.

The precise mechanism of this phenomenon is not fully understood, but itis believed to be caused partly by specular reflection at flat angles ofillumination near the extreme tips of the grains, which denies entry ofthis portion of incident light into the interior of the translucent ortransluminescent" grain, from whence it would ordinarily be glowinglyand diffusedly reflected back to the photocell. Since less light getsback from the grain ends, a spurious dark spot is signalled. Alsobelieved to be a cause, is the fact that less light is directlyreflected back to the photocell from irregularities on the surface ofthe ends of the grain, where the surface is at a different angle thanthat of the long stretch of the mid-portion of the grain. In any event,it has been found experimentally that with only one lamp forillumination, spurious signals do appear.

Accordingly, the invention contemplates the use of at least two lightsources 51 and 52 mounted respectively above and below the viewing means33, 34 so as to provide extra illumination to the ends of the ricegrain. The leading end of the grain is given extra illumination by lightsource 52 to compensate for the loss in illumination that the leadingend receives from light source 51. As for the mid-portion of the grain13, the combined illumination it receives and reflects to the photocellfrom both light sources adds up to produce a signal of the same generalvoltage level as that received from the leading end as a result of themore direct illumination of light source 52 above. A similar effect isproduced by light source 51 on the trailing end of the grain. The resultis an undisturbed steady voltage level signal 40 as the acceptable grainenters the viewing zone, passes through it, and departs. Only ifa grainwith a true dark spot appears does the photocell produce a deviatingpositive signal 43 to initiate rejection of the defective grain.

Upon receiving a rejection signal 43, the programmed logic of anelectronic controller 56 causes the operation of a compressed-air value57 and nozzle 58 to emit a quick sharp brief jet or blast of airdirected against the side of the grain 13 transversely to the path 31 soas to blow the defective grain along a deviating or deflected path 59into a reject hopper 61. If, however, the grain 31 is not defective andno signal pulse 43 is produced, the grain continues along path 31 to anacceptable product tube 62, which is laterally elongated so as to becommon to all channels, and may in turn be coupled to a bag or otherpackaging, transporting or storage apparatus.

In the illustrated apparatus, the light sources 35, 51 and 52 arefluorescent tubes operated at high frequency (e.g., 2O kilohertz) andhaving the ballasts synchronized as by a common coupling 60.

Occasionally, while the apparatus is operating, it is desirable to beable to sample the product that is being accepted in each individualchannel of the machine. For this purpose, the tube 62 (FIGS. 8 and 9) isformed with a side opening 63, and a number of individual sampling tubes64 are mounted to cover the opening 63 in the normal operating conditionof the machine, but without interfering with the flow of grainsdownwardly through the tube 62. The sampling tubes 64 are pivoted as at66 however, so that the upper ends 67 can be individually tippedinwardly to catch the grains and divert them outwardly through thenow-protruding open lower ends 68 and into the hand of the sampler.

Referring now to FIG. 7, an alternative arrangement is shown for usewith opague products that must be examined from both sides. A pair ofphotoelectric examining devices 33a and 33b are placed on opposite sidesof the path 31 from slide 11, and each phototube has a pair of lightsources 51a, 52a, 51b and 52b, respectively, associated therewith, aboveand below the phototube. Each phototube is directed toward a background36a and 36!), respectively, shown in the FIG- URE as fixed in position.Alternatively, adjustable backgrounds such as background 36 of FIG. 5could be used. Finally, a compressed air-jet nozzle 58a is mounted abovethe viewing zone 32a, as shown.

What is claimed is: l. A semi-free-fall sorting apparatus for granularitems, comprising:

an elongated slide tapering downwardly to the diameter of said items andhaving a central longitudinal generatrix that is steeply inclined forgravity separation of said granular items sliding downwardly thereon,and for aligning said sliding items in serial order along a common pathcorresponding to said central generatrix;

the upper end of said slide having a gently rounded bottom portion asseen in cross-section along the line of said central generatrix, thecurvature radius of said bottom portion being substantially greater thanthe mean radius of said granular items;

said slide tapering from upper to lower end so that the cross sectionalong the direction of said central generatrix at the lower end displaysa curved bot tom portion of curvature radius substantially in the sameorder as said mean radius of said granular items;

means for introducing said items in a random shower into the upper endportion of said slide; and

means for examining and sorting said items aligned in said serial order.

2. An apparatus as recited in claim 1 wherein:

said slide has spaced side walls extending from said curved bottomportion to define a U-shaped cross section at said upper end;

said side walls being angled to converge downwardly toward one anotherto define a generally V-shaped cross section at said lower end.

3. Apparatus as recited in claim 1 wherein:

said means for introducing said items to the upper end of said slideincludes a vibrating tapered chute in the same vertical plane as saidslide but gently inclined in the opposite direction so as to dischargesaid granular items into said slide with the least possible verticalcomponent of velocity and a horizontal component of velocity oppositelydirected to the horizontal velocity component that is to be induced insaid items by said slide.

4. The combination recited in claim 3, wherein said apparatus alsoincludes:

a plurality of said slides and said examining and sorting means arrangedin parallel and a corresponding plurality of said chutes also inparallel;

said chutes extending from a common feeding tray mounted for vibration;

motor and eccentric mass vibrating means mounted to vibrate said trayand chutes; and

each of said chutes having an adjustable gate at the tray end thereof toequalize the flow rate of said items despite differences in thevibrating effect resulting from differences in the chutes and theirdistances from the vibrating means.

5. The combination recited in claim 4, wherein said apparatus alsoincludes:

stationary hopper means mounted above said tray for reception of saidgranular items;

flexible coupling means between said hopper means and said tray;

said hopper means, flexible coupling means and tray being arranged todefine a closed conduit for said granular items from the entrance tosaid hopper means to the opening of said adjustable gates to saidchutes.

6. The combination recited in claim 5, wherein:

said slides are arranged in two criss-crossed banks;

the chutes for said respective banks extending from opposite sides of afeeder tray and hopper means;

said examining and sorting means being arranged in two correspondingbanks beneath said slides.

7. The combination recited in claim 1, wherein said examining andsorting means includes;

photoelectric viewing means disposed beside said path for viewing a zoneof said path no longer than the mean length of said granular items intheir sliding orientation with respect to said slide;

at least two light sources disposed respectively above and below saidphotoelectric means along the length of said path;

ejection means adjacent said path for selectively diverting said itemstherefrom upon signal from said photoelectric means;

receptacle means on said path below said ejection means for receivingundiverted items;

a third light source positioned on the opposite side of said path fromsaid viewing means and shielded from said viewing zone;

variable background means positioned adjacent said path directlyopposite said viewing means and illuminated by said third light sourceand adjustable to induce a signal from said photoelectric means that issubstantially identical to the signal induced by passage of themid-portion of an acceptable one of said items;

said ejection means being adapted to operate only when the signal fromsaid photoelectric means differs appreciably from saidbackground-induced signal;

said background means including a flat-surfaced background uniformlycolored in the same general color as said acceptable items;

said background being rotatably adjustable about an axis abnormal tosaid flat-surface so as to deepen or lighten the apparent shade of saidbackground as viewed by said photoelectric means, thus to induce saidsignal identical with that of an acceptable item.

8. The combination recited in claim 7 and adapted for the sorting ofelongated gray-white rice grains as said items, wherein:

said background is of generally gray-white color and is rotatable toreflect light to said photoelectric means in the same intensity as anacceptable grain of said rice;

said ejection means being calibrated to operate upon reception of asignal indicating a dark spot in one of said rice grains, said signalhaving a voltage amplitude level differing appreciably from thatprovided by said background.

9. The combination recited in claim 7, wherein:

two of said viewing means are provided on opposite sides of said pathfor viewing opaque items; and four light sources are provided, one aboveeach viewing means, and one below each viewing means; and two backgroundmeans are provided, each aligned with one of said viewing means and saidviewing zone.

10. The combination recited in claim 7, wherein said receptacle meansfor receiving acceptable undiverted items includes:

a first elongated tube aligned on said path and having an opening in theupper side thereof; and

a second elongated tube pivoted on the upper side of said first tube soas to cover said opening in a normal position of said second tubealigned parallel to said first tube;

said second tube being pivotable to a sampling position wherein theupper end of said second tube intrudes through said opening into saidfirst tube and diverts said acceptable items into said second tube forexamination as a sample.

1. A semi-free-fall sorting apparatus for granular items, comprising: anelongated slide tapering downwardly to the diameter of said items andhaving a central longitudinal generatrix that is steeply inclined forgravity separation of said granular items sliding downwardly thereon,and for aligning said sliding items in serial order along a common pathcorresponding to said central generatrix; the upper end of said slidehaving a gently rounded bottom portion as seen in cross-section alongthe line of said central generatrix, the curvature radius of said bottomportion being substantially greater than the mean radius of saidgranular items; said slide tapering from upper to lower end so that thecross section along the direction of said central generatrix at thelower end displays a curved bottom portion of curvature radiussubstantially in the same order as said mean radius of said granularitems; means for introducing said items in a random shower into theupper end portion of said slide; and means for examining and sortingsaid items aligned in said serial order.
 2. An apparatus as recited inclaim 1 wherein: saiD slide has spaced side walls extending from saidcurved bottom portion to define a U-shaped cross section at said upperend; said side walls being angled to converge downwardly toward oneanother to define a generally V-shaped cross section at said lower end.3. Apparatus as recited in claim 1 wherein: said means for introducingsaid items to the upper end of said slide includes a vibrating taperedchute in the same vertical plane as said slide but gently inclined inthe opposite direction so as to discharge said granular items into saidslide with the least possible vertical component of velocity and ahorizontal component of velocity oppositely directed to the horizontalvelocity component that is to be induced in said items by said slide. 4.The combination recited in claim 3, wherein said apparatus alsoincludes: a plurality of said slides and said examining and sortingmeans arranged in parallel and a corresponding plurality of said chutesalso in parallel; said chutes extending from a common feeding traymounted for vibration; motor and eccentric mass vibrating means mountedto vibrate said tray and chutes; and each of said chutes having anadjustable gate at the tray end thereof to equalize the flow rate ofsaid items despite differences in the vibrating effect resulting fromdifferences in the chutes and their distances from the vibrating means.5. The combination recited in claim 4, wherein said apparatus alsoincludes: stationary hopper means mounted above said tray for receptionof said granular items; flexible coupling means between said hoppermeans and said tray; said hopper means, flexible coupling means and traybeing arranged to define a closed conduit for said granular items fromthe entrance to said hopper means to the opening of said adjustablegates to said chutes.
 6. The combination recited in claim 5, wherein:said slides are arranged in two criss-crossed banks; the chutes for saidrespective banks extending from opposite sides of a feeder tray andhopper means; said examining and sorting means being arranged in twocorresponding banks beneath said slides.
 7. The combination recited inclaim 1, wherein said examining and sorting means includes;photoelectric viewing means disposed beside said path for viewing a zoneof said path no longer than the mean length of said granular items intheir sliding orientation with respect to said slide; at least two lightsources disposed respectively above and below said photoelectric meansalong the length of said path; ejection means adjacent said path forselectively diverting said items therefrom upon signal from saidphotoelectric means; receptacle means on said path below said ejectionmeans for receiving undiverted items; a third light source positioned onthe opposite side of said path from said viewing means and shielded fromsaid viewing zone; variable background means positioned adjacent saidpath directly opposite said viewing means and illuminated by said thirdlight source and adjustable to induce a signal from said photoelectricmeans that is substantially identical to the signal induced by passageof the mid-portion of an acceptable one of said items; said ejectionmeans being adapted to operate only when the signal from saidphotoelectric means differs appreciably from said background-inducedsignal; said background means including a flat-surfaced backgrounduniformly colored in the same general color as said acceptable items;said background being rotatably adjustable about an axis abnormal tosaid flat-surface so as to deepen or lighten the apparent shade of saidbackground as viewed by said photoelectric means, thus to induce saidsignal identical with that of an acceptable item.
 8. The combinationrecited in claim 7 and adapted for the sorting of elongated gray-whiterice grains as said items, wherein: said background is of generallygray-white color and is rOtatable to reflect light to said photoelectricmeans in the same intensity as an acceptable grain of said rice; saidejection means being calibrated to operate upon reception of a signalindicating a dark spot in one of said rice grains, said signal having avoltage amplitude level differing appreciably from that provided by saidbackground.
 9. The combination recited in claim 7, wherein: two of saidviewing means are provided on opposite sides of said path for viewingopaque items; and four light sources are provided, one above eachviewing means, and one below each viewing means; and two backgroundmeans are provided, each aligned with one of said viewing means and saidviewing zone.
 10. The combination recited in claim 7, wherein saidreceptacle means for receiving acceptable undiverted items includes: afirst elongated tube aligned on said path and having an opening in theupper side thereof; and a second elongated tube pivoted on the upperside of said first tube so as to cover said opening in a normal positionof said second tube aligned parallel to said first tube; said secondtube being pivotable to a sampling position wherein the upper end ofsaid second tube intrudes through said opening into said first tube anddiverts said acceptable items into said second tube for examination as asample.